Substrates, such as semiconductor wafers or flat panel displays, are typically processed in multiple steps. Many of these steps require the measurement and inspection of surface characteristics. Surface measurement and inspection typically are performed using a stage that moves the substrate so that the entire surface of the substrate can be measured or inspected. For accurate measurements, a stage must be capable of moving a substrate with high accuracy, i.e. capable of positioning with an accuracy of ±1 to 5 μm.
One type of stage used in measuring and inspecting substrates is an X-Y stage, which can move a substrate in two independent orthogonal directions, X and Y, to select an area on a substrate for viewing, imaging, or measurement. However, the footprint of an X-Y stage must be at least twice the diameter of the substrate to be measured in both the X and Y direction. Consequently, an X-Y stage requires a large area, particularly if 300 mm substrates are being inspected.
Another type of stage used in the measuring of substrates is a polar coordinate stage, otherwise known as an R-θ stage. R-θ stages move a substrate in a single linear direction (R-motion) and also rotate the stage (θ-motion). By moving the substrate in the R direction and rotating the substrate, any area on the substrate surface may be appropriately positioned for viewing, imaging, or measuring.
As described above, substrate measurement and inspection requires linear motion of a stage in at least one direction. One method to create linear motion is to translate rotary motion into linear motion. The prior art discloses a device that converts rotary motion into linear motion using a system of belts and pulleys, as is described in U.S. Pat. No. 4,897,015. However, this is a complicated design that is not easily adapted for use in the highly precise measurements of substrates on a stage.
Some substrates, e.g., semiconductor wafers, are very sensitive to environmental conditions. Accordingly, during processing, it is often desirable to inspect a substrate without altering the environmental conditions, e.g., the substrate could be measured within the processing chamber.
Thus, what is needed is a precision stage with a compact design that can accommodate substrates, including small or large substrates, and that is compatible for use in a chamber environment so as to eliminate contamination problems.